There is a rising interest on producing new renewable energy, especially, energy using biomass, due to the depletion of fossil fuels and CO2 saving effort all around the world. Among various biomass resources, lignocellulosic biomass has an advantage in that the shortfall in lignocellulosic biomass is the biggest and there are no ethical issues because lignocellulosic biomass is not irrelevant to the foodstuffs. Therefore, the production and development of the second-generation useful bio products using lignocelluloses that are lignocellulosic resources.
Lignocellulosic biomass is largely composed of lignin, cellulose, and hemicelluloses, which are carbohydrates.
It is known that lignin is a polymer having a large molecular weight including a large amount of aromatic compounds, in which methoxylated p-coumacyl alcohol, coniferylalcohol, synapyl alcohol, and the like are polymerized, and the decomposition of lignin is the most difficult among the natural compounds in the natural world. It is also known that cellulose is a polysaccharide prepared by binding glucoses with 1,4-linkage, and has a linear structure, so as to be in a stable type, thereby having physically and chemically strong structure. Hemicelluloses are a polysaccharide having low degree of polymerization of sugar as compared with cellulose, is mainly composed of xylan that is a polymer of xylose that is pentose, and furthermore, is composed of arabinose that is pentose, mannose, galactose, and glucose that are hexose.
The production of biomass using lignocellulosic biomass requires pretreatment, saccharification, and fermentation. Among them, the processes for improving the reaction rate and yield of enzymatic hydrolysis are commonly called the pretreatment. According to the pretreatment, the complex of lignin, cellulose, and hemicelluloses, which is a non-degradable aromatic polymer, is decomposed to reduce a degree of crystallization, increase the accessibility of enzyme, and increase the specific surface area of biomass, thereby increasing the amount of the effective enzyme. According to the degree of the pretreatment efficiency, the cost of preparing biomass is determined. Therefore, the pretreatment is one of the important factors for producing biomass.
As the pretreatment and saccharification for promoting the fermentability of lignocellulosic biomass, there is a method using a physical and chemical enzyme, which requires hydrolysis for obtaining the monosaccharide of pentose or hexose as a useful fermentable saccharificated product capable of being used by microorganisms from biomass materials. According to the method, lignin is typically penetrated by increasing the content of cellulose and decreasing the crystallinity of microfilament, and the reactivity and hydrolysis ability of hemicelluloses are increased by increasing the accessibility and the adsorption rate of cellulose hydrolase per unit area.
As a physically pretreatment, there are a ball milling, an ultrasonic milling, homogenization, and the like. According to the physically pretreatment, the particle size of biomass material is decreased to increase a specific surface area, and decrease the degree of polymerization of cellulose. However, the energy consumption thereof is high, and thus, the physical pretreatment is not favorable.
In addition, a chemical pretreatment is a hydrolysis using an acid and base, and is usually used in the pretreatment of biomass. However, according to the chemical pretreatment, the monosaccharides are not only produced, but toxic materials, for example, furfural, vanillin, weak acids, such as, ferulic acid and coumaric acid, furan derivatives, and phenolic compounds, that may seriously affect the growth of microorganism, may be induced so as to greatly affect on reducing the efficiency of the following fermentation. Therefore, a detoxification process is required to remove inhibitors from the substrate as the previous process before the fermentation.